Thermal degradation of cellulose and its phosphorylated products in air and nitrogen

The thermal degradation of cellulose and its phosphorylated products (phosphates, diethylphosphate, and diphenylphosphate) were studied in air and nitrogen by differential thermal analysis and dynamic thermogravimetry from ambient temperature to 750°C. From the resulting data various thermodynamic parameters were obtained following the methods of Broido and Freeman and Carroll. The values of E_a for decomposition for phosphorylated cellulose were found to be in the range 55–138 kJ mol^?1 in air and 85–152 kJ mol^?1 in nitrogen and depended upon the percent of phosphorus contents in the samples. The mass spectrum of cellobiose phosphate indicated the absence of the molecular ion, indicating that the compound was thermally unstable. The IR spectra of the pyrolysis residues of cellulose phosphate gave indication of formation of a compound having C?O and P?O groups. A fire retardancy mechanism for the thermal degradation of cellulose phosphate has been proposed.     

Thermal,morphological and spectroscopic studies on cellulose modified with phosphorus,nitrogen, sulphur and halogens

The kinetics of the thermal degradation of cellulose and modified cellulose, namely, cellulose phosphate, cellulose carbanilate, cellulose tosylate, chlorodeoxycellulose, bromodeoxycellulose, and iododeoxycellulose in air were studied by thermogravimetry and differential thermal analysis from ambient temperature to 700°C. The various thermodynamic functions for different stages of thermal degradation had been obtained following the procedure of Broido. The activation energies for the oxidative decomposition of cellulose and modified celluloses were found to be in the range 30–399 kJ mol^?1. The infrared spectra of the residues of modified celluloses gave indication of formation of a compound containing P?O, P? O? P (only in the case of cellulose phosphate), C?C, and C?O groups in the final residual char. The EPR signals indicated the formation of trapped and stable free radicals in the thermal degradation of all the compounds, particularly halodeoxycelluloses showed generation of large amounts of trapped free radicals during the oxidative decomposition. Scanning electron micrographs of the thermally degraded cellulose derivatives show changes in the fibrillar structure, evolution of gasesous products, and film formation depending upon the nature of the substituent in the cellulose matrix. The mechanism of thermal degradation of these compounds has been proposed.     

Kinetics of isothermal and non‐isothermal degradation of cellulose: model‐based and model‐free methods

BACKGROUND: The kinetics of the thermal decomposition of cellulosic materials is of interest from the viewpoint of flame retardancy for safety, optimization of incineration processes and reducing energy production from fossil sources and associated pollution. One essential step in these processes is the thermal degradation through mass and energy transport, which determines the rate of evolution of various types of products from cellulosic materials. RESULTS: Kinetic parameters have been determined using various model‐based and model‐free methods in the thermal degradation of cellulose up to 700 °C in helium atmosphere. The values of the activation energy obtained in isothermal processes and non‐isothermal processes have been found to be not far from each other. From the integral method, the random nucleation (F₁)‐type mechanism has been found most probable for cellulose degradation having an activation energy, E_a, in the range 156.5–166.5 kJ mol^?1, lnA = 20–23 min^?1, for first‐order reaction during its decomposition process at heating rates of 2, 5 and 10 °C min^?1. Based on the high correlation coefficient, many types of mechanisms seem equally good for non‐isothermal degradation of cellulose. CONCLUSION: The linear correlation coefficient has a limitation for verifying the correctness of a reaction mechanism in the study of degradation kinetics. Therefore, the correctness of a mechanism should be considered on the basis of comparing the kinetic parameters obtained from isothermal as well as non‐isothermal methods. Copyright © 2008 Society of Chemical Industry     

Thermal,spectral and morphological studies on cellulose,cellulose ethylthiophosphate and its metal complexes in air

Metal complexes of thiophosphorylated cellulose, when heated, give rise to high char yields. These and related observations suggest that such derivatisation may give rise to novel flame retardant treatments for cellulosic materials. The kinetics of thermal degradation of cellulose, cellulose ethylthiophosphate (CESP) and metal complexes of the CESP have been studied by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 700°C in dynamic air to investigate the potential flame retardance of the CESP and its metal complexes. Various parameters such as energy, entropy, enthalpy and free energy of activation have been calculated using the Broido method and transition state theory. For the decomposition stage of thermal degradation, the activation energies of the CESP samples lie in the range 53-133 kJmol^?1 and of the metal complexes, 108-177kJmol^?1, which are found to be lower than that of cellulose (187 kJmol^?1). Scanning electron micrographs of the CESP show that the fibrillar structure of cotton has become more evident and chars retain the general morphology of the original fibre although severe, localised zones of damage reflect the gross chemical and physical changes occurring during pyrolysis. The IR spectra of chars of modified samples indicate formation of compounds containing C=O, C=C and P=O groups. The mechanisms of thermal degradation of the CESP and its metal complexes have been proposed.     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Thermal decomposition of cellulose ethers

The thermostability and thermal decomposition kinetics of methyl cellulose (MC), ethyl cellulose (EC), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and hydroxypropyl–methyl cellulose (HPMC) were characterized in nitrogen and air by thermogravimetry (TG). Various methods of kinetic analysis were compared in case of thermal degradation of the five cellulose ethers. The initial decomposition temperature (T_d), temperature at the maximum decomposition rate (T_dm), activation energy (E), decomposition reaction order (n), and pre-exponential factor (Z) of the five cellulose ethers were evaluated from common TG curves and high-resolution TG curves obtained experimentally. The decomposition reactions in nitrogen were found to be of first order for MC, EC, and HPMC with the average E and ln Z values of 135 kJ/mol and 25 min⁻¹, although there were slight differences depending on the analytical methods used. The thermostability of cellulose ethers in air is substantially lower than in nitrogen, and the decomposition mechanism is more complex. The respective average E, n, ln Z values for HEC in nitrogen/air were found to be 105/50 kJ/mol, 2.7/0.5, and 22/8.3 min⁻¹, from constant heating rate TG method. The respective average E, n, and ln Z values for three cellulose ethers (EC/MC/HPMC) in air are 123/144/147 kJ/mol, 2.0/1.8/2.2, 24/28/28 min⁻¹ by using high-resolution TG technique. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2927–2936, 1999     

Thermal degradation studies of cellulose phosphates and cellulose thiophosphates

The thermal degradation of cellulose, cellulose phosphates, and cellulose thiophosphates was studied by differential thermal analysis, dynamic thermogravimetry, and derivative thermogravimetry from ambient temperature up to 750°C. Various thermodynamic parameters for different stages of thermal degradation of cellulose and its derivatives have been obtained following the methods of Broido, and Freeman and Carroll. Infrared spectra of thermally degraded samples were obtained. The data were analyzed in an effort to obtain more information concerning the flame-retardant mechanisms of cellulose phosphates and cellulose thiophosphates. Lower values of decomposition temperatures and activation energies of decomposition and higher char yields of cellulose phosphates as compared to cellulose lead to the conclusion that cellulose phosphorus esters are good flame retardants, and this property is retained even when these esters were subjected to ion exchange by Na⁺ and K⁺ ions. However, with the introduction of sulphur atoms, there was some decrease in this property.     

Synthesis and characterization of the new cellulose derivative films based on the hydroxyethyl cellulose prepared from esparto “stipa tenacissima” cellulose of Eastern Morocco. II. Esterification with acyl chlorides in a homogeneous medium

Esparto “Stipa tenacissima” cellulose esters derivatives: HECA‐COO? C₄H₈? COOC₂H₅, HECA‐COO? C₈H₁₆? COOC₂H₅, and HECA‐COO? C₆H₄? COOC₂H₅ were successfully prepared in Tetrahydrofuran (THF)/triethylamine system with a degree of substitution (DS), respectively, DS_AD‐Et=0.32, DS_SB‐Et=0.22, and DS_TRP‐Et=0.50 using hydroxyethyl cellulose acetate (HECA; DS_AC=0.50) as intermediate product, and we avoided the drawbacks of cellulose solubility. The structural modifications were investigated using Fourier transform infrared spectroscopy (FTIR), Proton nuclear magnetic resonance (¹H‐NMR), Carbon‐13 nuclear magnetic resonance (¹³C‐NMR), and Distortionless Enhancement by Polarization Transfer 135° (DEPT‐135). The results from these analyses revealed the presence of the characteristic groups indicating that the grafting reaction was successful. The crystallinity and the structure order changes during the esterification reactions were recorded by X‐ray diffraction (XRD), it is found that the crystallinity degree decrease from 63.1% for Esparto “Stipa tenacissima” cellulose to 27.74% for HECA. The thermal stability of the esterified and unmodified cellulose samples was studied by thermogravimetric analysis (TGA)‐differential thermal analysis (DTA); the modified HECA exhibits a decrease in thermal stability relatively to the unmodified HECA, and this may be related to the groups grafted. The resulted cellulose esters HECA‐P_x (x = 1, 2, or 3) were soluble in THF and present an amorphous structure justified by XRD spectra. It was noted by TGA‐DTA analysis that the cellulose esters with low melting range were proved as thermoplastic polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The pyrolysis of cellulose derivatives

The thermal degradation in vacuo of ethyl cellulose and cellulose acetate in the form of very thin films or bulk material between 230° and 320°C has been studied. With the ethyl cellulose films, volatilization (as measured by weight loss) was a first-order process up to about 50% reaction, with an activation energy of 208 kJ/mole. This is about the same as that associated with the initial drop in intrinsic viscosity of the solid during bulk pyrolysis, in which very high molecular weight material, probably crosslinked, was formed at a later stage. The volatile products from ethyl cellulose included H₂O, CO, CO₂, C₂H₄, C₂H₆, C₂H₅OH, CH₃CHO, unsaturated aliphatic compounds, and furan derivatives. Acetic acid and acetyl derivatives of D -glucose were produced from cellulose acetate. It is suggested that the polymers degrade by radical chain mechanisms, and a number of possible elementary steps are proposed.     

Pyrolysis and combustion of cellulose. VII. Thermal analysis of the phosphorylation of cellulose and model carbohydrates during pyrolsis in the presence of aromatic phosphates and phosphoramides

Thermal gravimetric analysis, differential scanning calorimetry, and derivative thermal gravimetric analysis were utilized to characterize the thermal interactions between cellulose, 1-6, anhydro β-D-glucopyranoside, and D-glucose and model phosphate and phosphoramide flame retardants. The phosphoramides induced higher char yields than the phosphates during the pyrolysis of the mixtures of carbohydrates and organophosphorus compounds. Exothermic reactions attributed to phosphorylation and char formation were observed with each of the phosphoramide/carbohydrate mixtures and were absent with the phosphates. The individual phosphorus compounds studied showed similar thermal behavior with each of the carbohydrates indicating that the mode of interaction for these mixtures was similar. Isothermal gravimetric analysis of the organophosphorus/carbohydrate mixtures was used to measure the rate of decomposition weight loss from isothermal conditions. This weight loss was used as an indication of rate of fuel formation. The kinetics observed for these measurements indicated that the phosphoramide mixtures underwent a rapid weight loss to a final char with an effective E_act of about 55 kcal/mol while the phosphate mixtures exhibited effective E_act′s for decomposition lower than those observed for the pure carbohydrates. Mixtures of glucose with selcted arylphosphoramide esters were pyrolysed in order to determine the effect of lability of the leaving group on char formation. Gas chromatographic analysis of the pyrolysis products indicated that phenol was the favored leaving group in comparison with aniline units, but char promotion appeared to be dependent on the number of P-N bonds present in the original phosphoramide. Electron spectroscopy for chemical analysis indicated that chemically similar chars were obtained from the different organophosphorus/carbohydrate combinations.     

Thermal and spectroscopic studies on flame-retardant cotton cellulose modified with THPC-urea-ADP and its transition metal complexes

Cotton cellulose has been treated with tetrakis(hydroxymethyl)phosphonium chloride (THPC), urea and small amounts of ammonium dihydrogen orthophosphate (ADP) to impart flame retardancy. Complexes of cell-THPC-urea-ADP with transition metals such as chromium, manganese, iron, cobalt, nickel, copper and zinc have been characterized by reflectance UV-visible spectra. The samples were subjected to differential thermal analysis and thermogravimetry from ambient temperature to 700°C in air to study their thermal behaviour. From the resulting data, various kinetic parameters for different stages of thermal degradation were obtained following the method of Broido. For the decomposition of cellulose and flame-retardant celluloses, the activation energy was found to increase from 242 to 322kJ mol^?1, the entropy of activation from 140 to 307 JK^?1 mol^?1 and the char yield from 2.5 to 31%. The free energy of activation for decomposition of cellulose and its derivatives was almost the same, viz. 148–162 kJ mol^?1, indicating that the basic steps in the decomposition of cellulose and its derivatives are the same. The IR spectra of the thermally degraded residues of cell-THPC-urea-ADP and its metal complexes indicate that dehydration takes place and a compound containing the carbonyl group is formed. The electron paramagnetic resonance signals indicate the formation of trapped and stable free radicals in the thermal degradation of cellulose and its derivatives.     

Aerobic biodegradation of cellulose acetate

Two separate assay systems were used to evaluate the biodegradation potential of cellulose acetate: an in vitro enrichment cultivation technique (closed batch system), and a system in which cellulose diacetate (CDA) films were suspended in a wastewater treatment system (open continuous feed system). The in vitro assay employed a stable enrichment culture, which was initiated by inoculating a basal salts medium containing cellulose acetate with 5% (v/v) activated sludge. Microscopic examination revealed extensive degradation of CDA (DS = 2.5) fibers after 2–3 weeks of incubation. Characterization of the CA fibers recovered from inoculated flasks demonstrated a lower average degree of substitution and a change in the mol wt profiles. In vitro enrichments with CDA (DS = 1.7) films were able to degrade > 80% of the films in 4–5 days. Cellulose acetate (DS = 2.5) films required 10–12 days for extensive degradation. Films prepared from cellulose triacetate remained essentially unchanged after 28 days in the in vitro assay. The wastewater treatment assay was less active than the in vitro enrichment system. For example, approximately 27 days were required for 70% degradation of CDA (DS = 1.7) films to occur while CDA (DS = 2.5) films required approximately 10 weeks before significant degradation was obtained. Supporting evidence for the biodegradation potential of cellulose acetate was obtained through the conversion of cellulose [1-¹⁴C]-acetate to ¹⁴CO₂ in the in vitro assay. The results of this work demonstrate that cellulose acetate fibers and films are potentially biodegradable and that the rate of biodegradation is highly dependent on the degree of substitution. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of the new cellulose derivative films based on the hydroxyethyl cellulose prepared from “Stipa Tenacissima” cellulose of Eastern Morocco. I. Solubility study

Hydroxyethyl cellulose Acetate (HECA) was prepared starting from hydroxyethyl cellulose (HEC), acetic anhydride and perchloric acid which was used as catalyst. The synthesized product was characterized by FTIR, ¹³C NMR, and ¹H NMR. Substitution degree (DS) of HECA was determined using FTIR spectra taking a classical titration method as reference. The ¹H NMR spectroscopy was also used to confirm the results obtained by FTIR. The DS is substantially affected by the temperature, the time of reaction and especially the equivalent number (eq. nb.) of the acetic anhydride added. We have studied and discussed in the context of usage in modification reactions, the solubility of the HECA samples by varying their DS. This investigation was based on the determination of the Flory‐Huggins interaction parameters (χ_SP) using the partial Hansen solubility parameters (HSP). HSP of HEC and the HECA samples were calculated from the Van‐Krevlen‐Hoftyze (VKH) method and the T. Lindvig approximation. We have focused our work on predicting and controlling family solvents of HECA with various DS, to facilitate and to optimize the homogenous modification reaction conditions. From results on a range of HECA samples, it is conclude that their prediction solubility taking the value of DS into account is possible, and then the surface modification can relatively be easily realized. The thermal analysis study shows some differences in T_g and thermal degradation between HEC and HECA, moreover these thermal temperatures are influenced by DS values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of cellulose graft copolymers. II. Cellulose–styrene graft copolymers synthesized by the ceric ion method

Styrene was graft-copolymerized onto wood cellulose by the ceric ion method of Mino and Kaizerman. The grafting reaction was found to depend strongly on the concentration of ceric ion in the grafting system and maximum grafting occurred in a narrow range of concentration of initiator, 1.0 × 10^?3-1.8 × 10^?3 mol/l, at 58 ± 1°C. A pretreatment technique, developed to enhance the monomer diffusion into cellulose, was found to increase the grafting considerably. The structures of the cellulose-styrene graft copolymers were studied by hydrolyzing away the cellulose backbone to isolate the grafted polystyrene branches. The molecular weight and the molecular weight distributions of the grafted polystyrene were determined using gel permeation chromatography. The number-average molecular weight (M?_n) ranged from 23,000 to 453,000 and the polydispersity ratios (M?_w/M?_n) varied from 2.5 to 8.0. The grafting frequencies calculated from the per cent grafting and molecular weight data were of the order of 0.05–0.4 polystyrene branches per cellulose chain.     

Isothermal transient current studies in cellulose acetate films

Step voltage transient current studies have been made in cellulose acetate films as a function of filed and thickness. A logarithmic plot (Scherr-Montroll plot) of the transient current vs. time gives a knee at a time t_T, which is interpreted as the transit time of the charge carrier. The value of the carrier mobility has been estimated to be 3.9 × 10^?9 cm².V^?1.S^?1 in cellulose acetate film. The carrier mobility in iodine-doped (2% w/w) cellulose acetate film has also been determined from Scher-Montroll plot and is found to be 3.3 × 10^?7 cm².V^?1.S^?1.     

Thermal softening and melting of esterified wood prepared in an N2O4–DMF cellulose solvent medium

The thermal softening and melting of a series of esterified wood samples, whose preparation has previously been described,⁴ have been studied by measuring the deformation of the samples under constant load at a constant heating rate. The introduction of acyl groups into wood including part of the original crystal structure in cellulose makes the modified wood meal conspicuously thermoplastic. While untreated dry wood shows a thermal softening point (T_s) of ca. 260°C, esterified wood meal samples with acyl groups larger than caproyl have a T_s of around 100°C or less, and appeared to melt over the temperature range of 220° to 250°C. In this case, the melting occurs even with wood meal samples esterified with appropriate acid chlorides in an N₂O₄–DMF–pyridine medium only for 30 min at room temperature. This might be the first finding that wood meal is converted, as a whole, into a thermoplastic material which can melt without any accompanying detectable degradation.     

H3PW12O40·4H2O as an efficient catalyst for the conversion of cellulose into partially substituted cellulose acetate

The preparation of partial acetylation of cellulose derived from rice straw was catalyzed by phosphotungstic acid with various numbers of crystal water, and H₃PW₁₂O₄₀·4H₂O was found to be as effective catalyst. The yield of the cellulose acetate was significantly enhanced by converting cellulose directly isolated from rice straw into microcrystalline cellulose before acetylation. The optimization of the acetylation was investigated by varying the amount of catalyst and acetic anhydride as well as reaction conditions including reaction time and medium, and a degree of substitution (DS) value of 2.29 and yield of 62.9% were obtained under the optimized conditions. The structure and the formation of the acetylated product were confirmed by Fourier transform infrared spectroscopy (FTIR) and powder X‐ray diffraction (XRD) technique, the thermal properties were determined by thermal analysis including thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC), and the morphology was observed by scanning electron microscope (SEM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41212.     

Hybrid composites based on technical cellulose from rice husk

We introduced the preparation of hybrid composites using technical cellulose as a matrix material from rice husks with a natural SiO₂ content from 0% to 19.4%. In this work, the physicochemical characteristics of the resulting hybrid composites have been investigated. The presence of Si? O? C chemical bonds in the resulting hybrid composites was determined by infrared spectroscopy. Microscopic analysis showed the complete removal of the mineral component and lignin from the cell wall of the rice husk fibers. This allows obtaining of an expanded surface of the fibers (101.7 m²/g) with uniform distribution of the TiO₂ aggregates. It could be shown that with content increasing of natural silicon dioxide in the hybrid composite the decomposition rate of H₂O₂ also increases. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45796.     

1,2‐propanediol–cellulose–acrylamide graft copolymers

1,2‐Propanediol–cellulose–acrylamide graft copolymers (PCACs) were developed for enhanced oil recovery. They were prepared with acrylamide and 1,2‐propanediol (PDO)–cellulose, which was formed through the addition of glycols to cellulose by the Shotten–Baumann reaction between 3‐chloro‐1,2‐propanediol and cellulose. The graft copolymerization was initiated with a redox system between Ce⁴⁺ and glycols in cellulose. The infrared spectrum of PDO–cellulose had some characteristic absorption bands around 2960 (νC? H) and 1050 cm^?1 (νC? O) that also appeared for the PDO group and pyranose ring of cellulose, respectively. The rate of Ce⁴⁺ consumption by PDO–cellulose was investigated through the calculation of the overall kinetic constant from the slopes of ln(D ? D_R) versus time (where D is the absorbance and D_R is the absorbance of the original polysaccharide solution) The results showed that PDO–cellulose had high reactivity and that there were two mechanisms of oxidation by Ce⁴⁺ with PDO–cellulose. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3022–3029, 2004     

Viscosity‐molecular weight relationship for cellulose solutions in either NMMO monohydrate or cuen

The intrinsic viscosities, [η], of nine cellulose samples, with molar masses from 50 × 10³ to 1 390 × 10³ were determined in the solvents NMMO*H₂O (N‐methyl morpholin N‐oxide hydrate) at 80°C and in cuen (copper II‐ethlenediamine) at 25°C. The evaluation of these results with respect to the Kuhn–Mark–Houwink relations shows that the data for NMMO*H₂O fall on the usual straight line in the double logarithmic plots only for M ≤ 158 10³; the corresponding [η]/M relation reads log ([η]/mL g⁻¹) = –1.465 + 0.735 log M. Beyond that molar mass [η] remains almost constant up to M ≈ 10⁶ and increases again thereafter. In contrast to NMMO*H₂O the cellulose solutions in cuen behave normal and the Kuhn–Mark–Houwink relation reads log ([η]/mL g⁻¹) = −1.185 + 0.735 log M. Possible reasons for the dissimilarities of the behavior of cellulose in these two solvents are being discussed. The comparison of three different methods for the determination of [η] from viscosity measurements at different polymer concentrations, c, demonstrates the advantages of plotting the natural logarithm of the relative viscosities as a function of c. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011